Method of fabricating a silicon solar cell

Abstract

A method of fabricating a back surface point contact silicon solar cell having p-doped regions and n-doped regions on the same side by forming a passivating layer on a surface of the cell having opened windows at the p-doped regions and the n-doped regions, b depositing and patterning a first metal layer on the passivating layer in such a way that the first metal layer comes into contact with the p-doped regions and the n-doped regions, by depositing a first insulator layer of polyimide on the first metal layer, by etching and patterning the first insulator layer of polyimide in such a way that the insulator layer has opened windows at, at least one of the p-doped regions and the n-doped regions, by depositing a second insulator layer of polyimide on the first insulator layer of polyimide, by etching and patterning the second insulator layer of polyimide in such a way that the insulator layer has opened windows at, at least one of the p-doped regions and the n-doped regions, by curing the first insulator layer of polyimide by heating at a predetermined second temperature for a predetermined second time, and by depositing a second metal layer on the second insulator layer of polyimide in such a way that the second metal layer comes into contact with the one of the p-doped regions and the n-doped regions. With this, the cell surface to be soldered onto a metallized substrate is well planarized and even to ensure sufficient conductibility, with less voids and less solder fatigue.

What is claimed is:  
     
       1. A method of fabricating a silicon solar cell having p-doped regions and n-doped regions on a same side, comprising the steps of: 
       (a) forming a passivating layer on a surface of the cell having opened windows at the p-doped regions and the n-doped regions;  
       (b) depositing and patterning a first metal layer on the passivating layer in such a way that the first metal layer comes into contact with the p-doped regions and the n-doped regions;  
       (c) depositing a first insulator layer of polyimide on the first metal layer;  
       (d) etching and patterning the first insulator layer of polyimide in such a way that the insulator layer has opened windows at, at least one of the p-doped regions and the n-doped regions;  
       (e) depositing a second insulator layer of polyimide on the first insulator layer of polyimide;  
       (f) etching and patterning the second insulator layer of polyimide in such a way that the insulator layer has opened windows at, at least one of the p-doped regions and the n-doped regions;  
       (g) curing the first and second insulator layers of polyimide by heating at a predetermined temperature for a predetermined time; and  
       (h) depositing a second metal layer on the second insulator of polyimide in such a way that the second metal layer comes into contact with the one of the p-doped regions and the n-doped regions.  
     
     
       2. A method of fabricating a silicon solar cell having p-doped regions and n-doped regions on a same side, comprising steps of: 
       (a) forming a passivating layer on a surface of the cell having opened windows at the p-doped regions and the n-doped regions;  
       (b) depositing and patterning a first metal layer on the passivating layer in such a way that the first metal layer comes into contact with the p-doped regions and the n-doped regions;  
       (c) depositing a first insulator layer of polyimide on the first metal layer;  
       (d) etching and patterning the first insulator of polyimide in such a way that the insulator layer has opened windows at, at least one of the p-doped regions and the n-doped regions;  
       (e) curing the first insulator layer of polyimide by heating at a predetermined first temperature for a predetermined first time;  
       (f) depositing a second insulator layer of polyimide on the first insulator layer of polyimide;  
       (g) etching and patterning the second insulator layer of polyimide in such a way that the insulator layer has opened windows at, at least one of the p-doped regions and the n-doped regions;  
       (h) curing the second insulator layer of polyimide by heating at a predetermined temperature for a predetermined time; and  
       (i) depositing a second metal layer on the second insulator layer of polyimide in such a way that the second metal layer comes into contact with the one of the p-doped regions and n-doped regions.  
     
     
       3. A method according to  claim 1 , wherein the second insulator layer is deposited in step (e) with a viscosity less than that of the first insulator layer deposited in step (c) to form a film thinner than that of the first insulator layer deposited in step (c). 
     
     
       4. A method according to  claim 2 , wherein the second insulator layer is deposited in step (f) with a viscosity less than that of the first insulator layer deposited in step (c) to form a film thinner than that of the first insulator layer deposited in step (c). 
     
     
       5. A method according to  claim 1 , wherein the second insulator layer is deposited in step (f) at a speed higher than that of the first insulator layer deposited in step (c). 
     
     
       6. A method according to  claim 1 , wherein the first insulator layer is deposited in step (c) to form a film having approximately the same thickness as the first metal layer deposited in step (b). 
     
     
       7. A method according  claim 1 , wherein the first insulator layer is etched and patterned in step (d) in such a way that the first insulator layer does not encroach on top of the first metal layer. 
     
     
       8. A method according  claim 1 , wherein the second insulator layer is etched and patterned in step (f) in such a way that the first insulator layer does encroach on top of the first metal layer. 
     
     
       9. A method according to  claim 2 , wherein the second insulator layer is deposited in step (f) at a speed higher than that of the first insulator layer deposited in step (c). 
     
     
       10. A method according to  claim 2 , wherein the first insulator layer is deposited in step (c) to form a film having approximately the same thickness as the first metal layer deposited in step (b). 
     
     
       11. A method according  claim 2 , wherein the first insulator layer is etched and patterned in step (d) in such a way that the first insulator layer does not encroach on top of the first metal layer. 
     
     
       12. A method according  claim 2 , wherein the second insulator layer is etched and patterned in step (g) in such a way that the first insulator layer does encroach on top of the first metal layer. 
     
     
       13. A method according to  claim 1 , wherein the second metal layer is deposited in step (h) at a thickness which is smaller than a thickness of the first metal layer deposited in step (b) and a thickness of the first and second insulator layer of polyimide deposited in steps (c) and (e). 
     
     
       14. A method according to  claim 2 , wherein the second metal layer is deposited in step (i) at a thickness which is smaller than a thickness of the first metal layer deposited in step (b) and a thickness of the first and second insulator layer of polyimide deposited in steps (c) and (f). 
     
     
       15. A method according to  claim 1 , wherein the second layer is made of a metal stack comprising an adhesion layer, a diffusion barrier and a solderable metal. 
     
     
       16. A method according to  claim 1 , wherein the second layer is made of a metal stack comprising a light reflective enhancement, an adhesion layer, a diffusion barrier and a solderable metal. 
     
     
       17. A method according to  claim 2 , wherein the second layer is made of a metal stack comprising an adhesion layer, a diffusion barrier and a solderable metal. 
     
     
       18. A method according to  claim 2 , wherein the second layer is made of a metal stack comprising a light reflective enhancement, an adhesion layer, a diffusion barrier and a solderable metal.